Why does the Battery was discharged to 0 Volt or drained compeletly ?.
A. Lithium batteries have self-discharge current, and also has the power consumption with BMS , so half-charged battery packs are generally required to be recharged every 3 months. and the Battery which was Discharge to the under-voltage protection value ,the Battery should be charged within 24H to Prevent the battery cell from being discharged to 0V or caused damage to the battery cell.

B. If there is a GPS module or Bluetooth module that is directly powered by B+ B-, then the battery pack cannot be placed for a long time. If the average power consumption of the GPS module is calculated as 10mA, it will consume 7200mAH of capacity if it is left for one month. Moreover, there is no undervoltage protection when connected to the B+ and B- terminal directly , wich will be very easy to discharge the battery pack to 0V.

C. The discharge MOS of the protection board has been broken ,the battery pack has no under-voltage protection, which will be easy for the Battery to be discharged compeletly to 0 Volt.